Note For complete syntax and usage information for the switch commands used in this chapter, look at the Cisco Catalyst 4500 Series Switch Command Reference and related publications at this location:

http://www.cisco.com/en/US/products/hw/switches/ps4324/index.html

If the command is not found in the Catalyst 4500 Command Reference, it is located in the larger Cisco IOS library. Refer to the Catalyst 4500 Series Switch Cisco IOS Command Reference and related publications at this location:

http://www.cisco.com/en/US/products/ps6350/index.html

Overview of Interface Configuration

By default, all interfaces are enabled. The 10/100-Mbps Ethernet interfaces autonegotiate connection speed and duplex. The 10/100/1000-Mbps Ethernet interfaces negotiate speed, duplex, and flow control. The 1000-Mbps Ethernet interfaces negotiate flow control only. Autonegotiation automatically selects the fastest speed possible on that port for the given pair. If a speed is explicitly stated for an interface, that interface will default to half duplex unless it is explicitly set for full duplex.

Many features are enabled on a per-interface basis. When you enter the interface command, you must specify the following:

•Interface type:

–Fast Ethernet (use the fastethernet keyword)

–Gigabit Ethernet (use the gigabitethernet keyword)

•Slot number—The slot in which the interface module is installed. Slots are numbered starting with 1, from top to bottom.

•Interface number—The interface number on the module. The interface numbers always begin with 1. When you are facing the front of the switch, the interfaces are numbered from left to right.

You can identify interfaces by physically checking the slot/interface location on the switch. You can also use the Cisco IOS show commands to display information about a specific interface or all the interfaces.

Using the interface Command

These general instructions apply to all interface configuration processes.

Step 2 In global configuration mode, enter the interface command. Identify the interface type and the number of the connector on the interface card. The following example shows how to select Fast Ethernet, slot 5, interface 1:

Switch(config)# interface fastethernet 5/1

Switch(config-if)#

Step 3 Interface numbers are assigned at the factory at the time of installation or when modules are added to a system. Enter the show interfaces EXEC command to see a list of all interfaces installed on your switch. A report is provided for each interface that your switch supports, as shown in this display:

Step 4 To begin configuring Fast Ethernet interface 5/5, as shown in the following example, enter the interface keyword, interface type, slot number, and interface number in global configuration mode:

Switch# configure terminal

Enter configuration commands, one per line. End with CNTL/Z.

Switch(config)# interface fastethernet 5/5

Switch(config-if)#

Note You do not need to add a space between the interface type and interface number. For example, in the preceding line you can specify either fastethernet 5/5 or fastethernet5/5.

Step 5 Follow each interface command with the interface configuration commands your particular interface requires. The commands you enter define the protocols and applications that will run on the interface. The commands are collected and applied to the interface command until you enter another interface command or press Ctrl-Z to exit interface configuration mode and return to privileged EXEC mode.

Configuring a Range of Interfaces

The interface-range configuration mode allows you to configure multiple interfaces with the same configuration parameters. When you enter the interface-range configuration mode, all command parameters you enter are attributed to all interfaces within that range until you exit interface-range configuration mode.

To configure a range of interfaces with the same configuration, perform this task:

Note When you use the interface range command, you must add a space between the vlan, fastethernet, gigabitethernet, or macro keyword and the dash. For example, the command interface range fastethernet 5/1 - 5 specifies a valid range; the command interface range fastethernet 1-5 does not contain a valid range command.

Note The interface range command works only with VLAN interfaces that have been configured with the interface vlan command (the show running-configuration command displays the configured VLAN interfaces). VLAN interfaces that are not displayed by the show running-configuration command cannot be used with the interface range command.

This example shows how to reenable all Fast Ethernet interfaces 5/1 to 5/5:

Switch(config)# interface range fastethernet 5/1 - 5

Switch(config-if-range)# no shutdown

Switch(config-if-range)#

*Oct 6 08:24:35: %LINK-3-UPDOWN: Interface FastEthernet5/1, changed state to up

*Oct 6 08:24:35: %LINK-3-UPDOWN: Interface FastEthernet5/2, changed state to up

*Oct 6 08:24:35: %LINK-3-UPDOWN: Interface FastEthernet5/3, changed state to up

*Oct 6 08:24:35: %LINK-3-UPDOWN: Interface FastEthernet5/4, changed state to up

*Oct 6 08:24:35: %LINK-3-UPDOWN: Interface FastEthernet5/5, changed state to up

This example shows how to use a comma to add different interface type strings to the range to reenable all Fast Ethernet interfaces in the range 5/1 to 5/5 and both Gigabit Ethernet interfaces 1/1 and 1/2:

If you enter multiple configuration commands while you are in interface-range configuration mode, each command is run as it is entered (they are not batched together and run after you exit interface-range configuration mode). If you exit interface-range configuration mode while the commands are being run, some commands might not be run on all interfaces in the range. Wait until the command prompt is displayed before exiting interface-range configuration mode.

Defining and Using Interface-Range Macros

You can define an interface-range macro to automatically select a range of interfaces for configuration. Before you can use the macro keyword in the interface-range macro command string, you must define the macro.

Speed and Duplex Mode Configuration Guidelines

You can configure the interface speed and duplex mode parameters to auto and allow the Catalyst 4500 series switch to negotiate the interface speed and duplex mode between interfaces. If you decide to configure the interface speed and duplex commands manually, consider the following:

•If you set the interface speed to auto, the switch automatically sets the duplex mode to auto.

•If you enter the no speed command, the switch automatically configures both interface speed and duplex to auto.

•When you set the interface speed to 1000 Mbps, the duplex mode is full duplex. You cannot change the duplex mode.

•If the interface speed is set to 10 or 100 mbps, the duplex mode is set to half duplex by default unless you explicitly configure it.

Caution Changing the interface speed and duplex mode configuration might shut down and restart the interface during the reconfiguration.

Setting the Interface Speed

If you set the interface speed to auto on a 10/100-Mbps Ethernet interface, speed and duplex are autonegotiated.

To set the port speed for a 10/100-Mbps Ethernet interface, perform this task:

Command

Purpose

Step 1

Switch(config)# interface fastethernetslot/interface

Specifies the interface to be configured.

Step 2

Switch(config-if)# speed [10 | 100 | auto]

Sets the interface speed of the interface.

This example shows how to set the interface speed to 100 Mbps on the Fast Ethernet interface 5/4:

Switch(config)# interface fastethernet 5/4

Switch(config-if)# speed 100

Turning off autonegotiation on a Gigabit Ethernet interface will result in the port being forced into 1000 Mbps and full-duplex mode. To turn off the port speed autonegotiation for Gigabit Ethernet interface 1/1, perform this task:

Command

Purpose

Step 1

Switch(config)# interface gigabitethernet1/1

Specifies the interface to be configured.

Step 2

Switch(config-if)# speednonegotiate

Disables autonegotiation on the interface.

To restore autonegotiation, enter the no speed nonegotiate command in the interface configuration mode.

Note For the blocking ports on the WS-X4416 module, do not set the speed to autonegotiate.

Setting the Interface Duplex Mode

Note When the interface is set to 1000 Mbps, you cannot change the duplex mode from full duplex to half duplex.

Note If you set the port speed to auto on a 10/100-Mbps Ethernet interface, both speed and duplex mode are autonegotiated. The configured duplex mode is not applied on autonegotiation interfaces.

To set the duplex mode of a Fast Ethernet interface, perform this task:

Command

Purpose

Step 1

Switch(config)# interface fastethernetslot/interface

Specifies the interface to be configured.

Step 2

Switch(config-if)# duplex [auto | full | half]

Sets the duplex mode of the interface.

This example shows how to set the interface duplex mode to full on Fast Ethernet interface 5/4:

Switch(config)# interface fastethernet 5/4

Switch(config-if)# duplex full

Displaying the Interface Speed and Duplex Mode Configuration

To display the interface speed and duplex mode configuration for an interface, perform this task:

Adding a Description for an Interface

You can add a description about an interface to help you remember its function. The description appears in the output of the following commands: show configuration, show running-config, and show interfaces.

To add a description for an interface, enter the following command:

Command

Purpose

Switch(config-if)# descriptionstring

Adds a description for an interface.

This example shows how to add a description on Fast Ethernet interface 5/5:

Understanding Jumbo Frame Support

Jumbo Frame Support Overview

A jumbo frame is a frame larger than the default Ethernet size. Enable jumbo frame support by configuring a larger-than-default maximum transmission unit (MTU) size on a port or interface.

Catalyst 4500 series switch Ethernet LAN ports configured with a nondefault MTU size accept frames containing packets with a size between 1500 and 9198 bytes. With a nondefault MTU size configured, the packet size of ingress frames is checked. If the packet is larger than the configured MTU, it is dropped.

For traffic that needs to be routed, the MTU of the egress port is checked. If the MTU is smaller than the packet size, the packet is forwarded to the CPU. If the "do not fragment bit" is not set, it is fragmented. Otherwise, the packet is dropped.

Note Jumbo frame support does not fragment Layer 2 switched packets.

The Catalyst 4500 series switch does not compare the packet size with the MTU at the egress port, but jumbo frames are dropped in ports that do not support them. The frames can be transmitted in ports that do support jumbo frames, even though the MTU is not configured to jumbo size.

Note Jumbo frame support is only configured per interface; jumbo frame support cannot be configured globally.

Ethernet Ports

With Cisco IOS Release 12.1(20)EW, configuring a nondefault MTU size on certain Ethernet port limits the size of ingress packets. The MTU does not impact the egress packets.

With releases earlier than Cisco IOS Release 12.1(13)EW, you can configure the MTU size only on Gigabit Ethernet and 10-Gigabit Ethernet ports.

Layer 3 and Layer 2 EtherChannels

With Release Cisco IOS Release 12.1(20)EW and later releases, you can configure all the interfaces in an EtherChannel provided that they have the same MTU. Changing the MTU of an EtherChannel changes the MTU of all member ports. If the MTU of a member port cannot be changed to the new value, that port is suspended (administratively shut down). A port cannot join an EtherChannel if the port has a different MTU. If a member port of an EtherChannel changes MTU, the member port is suspended.

VLAN Interfaces

If switch ports reside in the same VLAN, either configure all of the switch ports to handle jumbo frames and support the same MTU size, or configure none of them. However, such uniformity of MTU size in the same VLAN is not enforced.

When a VLAN has switch ports with different MTU size, packets received from a port with a larger MTU might be dropped when they are forwarded to a port with a smaller MTU.

If the switch ports in a VLAN have jumbo frames enabled, the corresponding SVI can have jumbo frames enabled. The MTU of an SVI should always be smaller than the smallest MTU among all the switch ports in the VLAN, but this condition is not enforced.

The MTU of a packet is not checked on the ingress side for an SVI; it is checked on the egress side of an SVI. If the MTU of a packet is larger than the MTU of the egress SVI, the packet will be sent to the CPU for fragmentation processing. If the "do not fragment" bit is not set, the packet is fragmented. Otherwise, the packet is dropped.

Interacting with the Baby Giants Feature

The baby giants feature, introduced in Cisco IOS Release 12.1(12c)EW, uses the global command system mtu <size> to set the global baby giant MTU. This feature also allows certain interfaces to support Ethernet payload size of up to 1552 bytes.

Both the system mtu command and the per-interface mtu command can operate on interfaces that can support jumbo frames, but the per-interface mtu command takes precedence.

For example, let's say that before setting the per-interface MTU for interface gi1/1, you issue the system mtu 1550 command to change the MTU for gi1/1 to 1550 bytes. Next, you issue the per-interface mtu command to change the MTU for gi1/1 to 9198 bytes. Now, if you change the baby giant MTU to 1540 bytes with the command system mtu 1540, the MTU for gi1/1 remains unchanged at 9198 bytes.

Understanding Online Insertion and Removal

The online insertion and removal (OIR) feature supported on the Catalyst 4500 series switch allows you to remove and replace modules while the system is online. You can shut down the module before removal and restart it after insertion without causing other software or interfaces to shut down.

You do not need to enter a command to notify the software that you are going to remove or install a module. The system notifies the supervisor engine that a module has been removed or installed and scans the system for a configuration change. The newly installed module is initialized, and each interface type is verified against the system configuration; then the system runs diagnostics on the new interface. There is no disruption to normal operation during module insertion or removal.

If you remove a module and then replace it, or insert a different module of the same type into the same slot, no change to the system configuration is needed. An interface of a type that has been configured previously will be brought online immediately. If you remove a module and insert a module of a different type, the interface(s) on that module will be administratively up with the default configuration for that module.

Monitoring and Maintaining the Interface

The following sections describe how to monitor and maintain the interfaces:

Monitoring Interface and Controller Status

The Cisco IOS software for the Catalyst 4500 series switch contains commands that you can enter at the EXEC prompt to display information about the interface, including the version of the software and the hardware, the controller status, and statistics about the interfaces. The following table lists some of the interface monitoring commands. (You can display the full list of show commands by entering the show ? command at the EXEC prompt.) These commands are fully described in the InterfaceCommand Reference.

To display information about the interface, perform this task:

Command

Purpose

Step 1

Switch# show interfaces [type slot/interface]

Displays the status and configuration of all interfaces or of a specific interface.

Step 2

Switch# show running-config

Displays the configuration currently running in RAM.

Step 3

Switch# show protocols [type slot/interface]

Displays the global (system-wide) and interface-specific status of any configured protocol.

Step 4

Switch# show version

Displays the hardware configuration, software version, the names and sources of configuration files, and the boot images.

This example shows how to display the status of Fast Ethernet interface 5/5:

Switch# show protocols fastethernet 5/5

FastEthernet5/5 is up, line protocol is up

Switch#

Clearing and Resetting the Interface

To clear the interface counters shown with the show interfaces command, enter the following command:

Command

Purpose

Switch#clear counters{type slot/interface}

Clears interface counters.

This example shows how to clear and reset the counters on Fast Ethernet interface 5/5:

The clear counters command (without any arguments) clears all the current interface counters from all interfaces.

Note The clear counters command does not clear counters retrieved with SNMP; it clears only those counters displayed with the EXEC show interfaces command.

Shutting Down and Restarting an Interface

You can disable an interface, which disables all functions on the specified interface and marks the interface as unavailable on all monitoring command displays. This information is communicated to other network servers through all dynamic routing protocols. The interface will not be mentioned in any routing updates.

*Sep 30 08:33:47: %LINK-5-CHANGED: Interface FastEthernet5/5, changed state to a
administratively down

Switch(config-if)#

This example shows how to reenable Fast Ethernet interface 5/5:

Switch(config-if)# no shutdown

Switch(config-if)#

*Sep 30 08:36:00: %LINK-3-UPDOWN: Interface FastEthernet5/5, changed state to up

Switch(config-if)#

To check whether or not an interface is disabled, enter the EXEC show interfaces command. An interface that has been shut down is shown as being administratively down when you enter the show interfaces command.